A thin-film solar-cell element comprising a rear electrode layer, a photoelectric conversion layer, a transparent electrode layer sequentially laminated on a substrate, wherein among a plurality of such thin-film photoelectric conversion elements, which admit light from the transparent electrode layer and convert it to electricity, the rear electrode layer, the photoelectric conversion layer, and the transparent layer are sequentially formed, but before disposing the next layer they are separated by various patterning processes to form a series connected structure, is disclosed, for example, in Japanese Patent Publication No. Hei 5-72113. One of the purposes of this series connection structure is, on the one hand, to obtain a high output voltage from one solar cell array and, on the other hand, to reduce the ohmic losses in the transparent electrode. By way of explanation, if the solar cell is formed as one unit over the entire surface of the substrate without forming the series connection structure, photo-generated carriers migrate over a long distance in the transparent electrode and the rear electrode to the output leads disposed at the ends of the solar cell.
The metallic electrode generally has a low resistance. As a result, resistive losses caused by the current flowing through the metallic electrode may be neglected. However, the sheet resistance of the transparent conductive thin-film may normally be as large as 5 to 30 ohms per square, hence resistive losses caused by the current flowing over a long distance in the transparent electrode layer cannot be disregarded. For this reason, conventional technology usually divides a large-area solar cell into a plurality of strip-formed cells, each with a width from 4 mm to 20 mm.
If a solar cell is partitioned into strip-formed cells connected in series, dead spaces that do not contribute to power generation are created at the connections, reducing the effective area for power generation and therefore the output from the solar cell. Thin-film solar cells, which are described in the specifications of the Japanese Patent Applications No. Hei 4-347394; No. Hei 5-78382; No. Hei 5-67976 and No. Hei 5-220870, in the names of the applicants, provide an auxiliary electrode layer disposed on the rear face of a flexible substrate of a plastic film or the like, in which the auxiliary electrode layer is connected through a connection hole to a rear electrode layer or a transparent electrode layer. Such series connection of solar cell units via the auxiliary electrode layer prevents reduction of the effective area for power generation.
The thin-film solar cell made of film type substrates features low material cost and mass producible which corresponds to a low production cost. The amorphous-silicon solar cell also features ease of formation of the integrated structure and therefore, design capability which ensures an arbitrary output voltage for a given area thereof The output voltage of the solar cell is varied depending upon the system design of an inverter or battery to be connected thereto. In mass production, however, varying the design voltage of the solar cell as required may lower the productivity thereof To mass-produce the solar cells of various output voltages, it is necessary to vary at will the voltage thereof in the later manufacturing processes of production.
The present invention is intended to solve the conventional problems discussed above, and provide a thin-film solar cell adaptable for providing the desired output voltage and applicable to mass production, and a method for the manufacture of such a solar cell.